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  Composite electrical brush constructionUSPTO Application #: 20070035196Title: Composite electrical brush construction Abstract: A method of manufacturing a composite electrical brush (10) comprises forming a brush body part (14) of low resistivity, carbon/graphite/resin material; heat treating the formed body; applying a layer (34) of high resistivity, resin-containing material to a face (22) of the brush body part; and curing the high resistivity layer: preferably the high resistivity layer is a paste, is applied by roll coating, painting, screen printing or transfer printing and can be applied to a surface (28) of the brush body part other than a surface (20, 24) of the press-way direction: the thus-formed composite electrical brush has the high resistivity, graphite/resin layer (34) bonded to the back face (28 ) of the carbon/graphite/resin brush body part (14). (end of abstract) Agent: Mccarter & English, LLP - Stamford, CT, US Inventor: David Hall Sidgwick USPTO Applicaton #: 20070035196 - Class: 310249000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070035196. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to methods of manufacturing composite electrical brushes and to composite electrical brushes manufactured thereby. Electrical brushes are a conductor serving to provide, at a sliding (usually rotating) surface, electrical contact with a part moving relatively to the brush: for example, brushes are used in the transfer of electricity from and/or to slip rings or commutators in electrical machines. BACKGROUND [0002] A composite electrical brush is a brush comprising two different materials laminated across the brush. Such brushes are sometimes referred to as sandwich brushes or bi-component brushes and give characteristics not achievable with a brush of uniform composition. The brush will usually have a flexible conductor or shunt (hereinafter "flex"), such as braided copper, located into one face of the brush to enable current transfer. [0003] A major application of composite electrical brushes is in commutation influence, composite electrical brushes with two or more layers of distinguishably different materials will have hybrid contact drop characteristics; this can be used to influence commutation. Typically in composite electrical brushes, a high copper part is the major portion having. the properties of relatively low electrical resistivity and a low copper part is the minor portion having relatively high resistivity. The low copper part forms the tailing edge of the brush so that during the commutation process the tendency for a spark to be created between the trailing edge of the brush and the departing commutator segment is minimised. Such brushes are commonly but not exclusively used in applications where high currents are passed and electrical wear plays a significant part in he commutation process such as in permanent magnet geared starters. [0004] Other reasons for laminating different materials across a brush include: [0005] Friction stabilisation--the provision of differing frictional characteristics to the laminated materials to provide smoother running of the brush without the need to incorporate so-called "lubricator" brushes among the main brushes on a machine. [0006] Collector skin control--the provision of abrasive layers to provide a cleaning action to remove skins of debris forming on the collector surface or between the conductors of a commutator. [0007] Circulating current impedance--the suppression of parasitic currents traversing the brush face. Transformer action circulating currents can be set up in the brushes in some applications and the resistance at the bond between the two layers may help suppress these. [0008] Typically, a composite electrical brush is made by adapting a standard press to take two filling shoes, one for each powder, and by modifying the stroke of the press to allow two filling actions. On occasion a pre-pressing compaction stroke, of a top tool, occurs between the two fillings. Finally the top tool and copper flexible is inserted into the die. The two powders are then pressed together and around the powders to make the final product. Alternately a pre-form, a pre-pressed piece of a single powder, may be inserted into the die. A second powder is added on top and the whole pressed, with copper flexible as described above. The brush is subsequently heat treated and finished. Typical finishing is to reduce the press-way direction to size, grind a radius on the running face and weld the flex, to prevent fraying and allow easy subsequent assembly. Because of the method of manufacture the thickness of the high resistivity part is typically 20% of the final brush thickness. Additionally, the choice of high resistivity material is limited to those that can be subjected to heat treatment required for the low resistivity main body part, typically 500.degree. C., and the need to match thermal expansion coefficients so that the materials do not separate in heat treatment. PRIOR ART [0009] Document GB-A-1509469 discloses a composite electrical brush with layers of graphited or ungraphited pyrolytic carbon attached to the body of a brush by an electrically conductive bond or depositing pyrolytic carbon on a face of the brush body from a vapour phase. [0010] Document U.S. Pat No. 5,285,126 discloses a press-moulded, composite electrical brush having a body made of a first carbon piece, and a layer disposed on a side thereof made of a second, less conductive carbon piece; the second piece covering only a portion of the side of the blush. OBJECT OF THE INVENTION [0011] It is an object of the present invention to provide an alternative and simpler method of manufacturing composite electrical brushes; which method, additionally, enables the manufacture of heretofore impossible composite-electrical brush designs. [0012] The applicant has realised that as the composite electrical brush has to be finished i.e. to reduce the press-way thickness to size etc, then it is possible to add the high resistivity layer as part of the finishing process and after the heat treatment process. This means that a wider range of materials can be used for the high resistivity layer and composite electrical brushes can be pressed on a standard mono press (i.e. one with a single filling shoe) and have a high resistivity layer applied subsequently. By such a procedure the high resistivity layer may be thinner than hitherto which may extend the range of devices in which such brushes may be used and applied to other than press-way direction brush surfaces. STATEMENT OF INVENTION [0013] Accordingly the present invention a method of manufacturing a composite electrical brush comprises the steps of: [0014] forming a brush body part of low resistivity, carbon/graphite/resin material; heat treating the brush body part to carbonise the resin; [0015] applying a layer of high resistivity, resin-containing material to a face of the brush body part; and; [0016] curing the high resistivity layer to bond it to the brush body part. [0017] In a preferred embodiment of the method of the present invention, the high resistivity, layer is a paste and may be applied by roll coating, painting, screen printing or transfer printing. [0018] In an further embodiment of the method of the present invention, the brush body part is pressed and the high resistivity layer may be applied to a surface of the brush body part other than a surface of the press-way direction. [0019] Also according to the present invention, a composite electrical brush comprises a high resistivity, graphite/resin layer bonded to a low resistivity, carbon/graphite/resin brush body part. [0020] According to a preferred embodiment of the present invention, the thickness of the high resistivity, graphite/resin layer is less than 10% of the brush body part thickness. [0021] According to another embodiment of the present invention, the brush body part is a pressing and the high resistivity layer is bonded to a surface of the brush body part other than a surface of the press-way direction. [0022] By low resistivity is meant a material having a resistivity of less than 50 .mu..OMEGA.m (microOhmmetre). By high resistivity is meant a material having a resistivity greater than 200 .mu..OMEGA.m. In addition the ratio of high to low resistivity may vary from 4:1 upward. BRIEF DESCRIPTION OF DRAWING [0023] The above and further features of the present invention are illustrated by way of example in the following description with reference to the drawing which is a perspective view of a composite electrical brush. DETAILED DESCRIPTION [0024] As shown by FIG. 1, a composite electrical blush 10 is shown contacting part of a commutator 12, the brush having a main body part 14 with a front face 16, an entering (leading) edge 18, a bevelled contact surface 20, a side face 22, a top surface 24, a leaving (trailing) edge 26, and a back face 28. A flex 30 is fitted into the top surface 24, is embedded in the brush body part and conducts current to/from the brush 10. Continue reading... Full patent description for Composite electrical brush construction Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Composite electrical brush construction patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Composite electrical brush construction or other areas of interest. ### Previous Patent Application: Brush holder apparatus, brush assembly, and method Next Patent Application: Outer rotor motor Industry Class: Electrical generator or motor structure ### FreshPatents.com Support Thank you for viewing the Composite electrical brush construction patent info. 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